Devices which measure psychological stress levels have been used as an indicator of deception and are commonly known as lie detection devices. Originally used in the field of law enforcement, these devices are now also commonly used in the military and the private sector. The first type of stress detection device, known as the polygraph, measures changes in a person's body functions related to the stress of deception, including changes in their heart rate, breathing, and electrodermal activity. In the beginning of polygraph examinations the person being tested had sensors placed on various parts of their body to measure the above noted functions and these sensors were in turn connected by wires to the polygraph device. A trained individual interpreted the output of the sensors to determine if the person being tested had exhibited any symptoms of stress indicative of uttering false statements. Present day polygraph devices are computer implemented. However, the basic technology of the device has changed very little.
Advances in the field of lie detection have been focused on the detection of stress in speech. These results could be used in a portable lie detection device which could be used “in the field.” The advantage of voice analysis over the polygraph is that the subject being tested does not have to be physically connected to the device and thus voice analysis is a non-invasive method of lie detection or truth verification.